[CrO<sub>4</sub>] Clusters as Dehydrogenation Terminators for Photocatalytic Oxidation of Methane to Achieve Nearly 100% Oxygenates Selectivity
Zhengfeng Shen, Jianxin Liu, Lijun Guo, Yawen Wang, Yunfang Wang, Xiao Zhang, Xuan Jian, Xiaoming Gao, Zhongde Wang, Caimei Fan, Rui Li, Jiancheng Wang
Abstract
The direct conversion of methane to high-value liquid oxygenates under mild conditions holds considerable appeal. However, a significant dilemma is that target oxygenates are highly susceptible to overoxidation due to the uncontrollable chain dehydrogenation process. This study reveals that various MCrO 4 (M = Bi, Pb, Ag 2, Ba, Cu) compounds exhibit 100% selectivity for methane oxidation to oxygenates, with Bi 8 (CrO 4 )O 11 showing the highest activity, producing 556.21 μmol g –1 and an apparent quantum efficiency of 1.54% at 350 nm. The [CrO 4 ] moiety functions as dehydrogenation terminators in the photocatalytic reaction, capturing methane oxidation intermediates and preventing overoxidation. In situ DRIFTS, XPS, and calculations show methane is activated to form oxidation intermediates at the [BiO x ] center, which then move to [CrO 4 ]. [CrO 4 ] exhibits an exceptionally high energy barrier (3.40 eV) for deep dehydrogenation, thereby halting the dehydrogenation of oxygenates. This work broadens the design and development of catalysts for inhibiting excessive oxidation of target products.